When loading a film cartridge, such as 35 mm film cartridge, into a camera, one must first determine whether or not the cartridge has been previously loaded and exposed. Many cameras automatically rewind an exposed cartridge of film such that no film leader is left protruding from the cartridge. A film cartridge with no leader generally indicates that the film in the cartridge has been exposed. However, many cameras do not automatically or completely rewind the exposed film into the cartridge, leaving the possibility of some film leader protruding from the cartridge. As such, there is not way to tell whether or not such a roll of film has been exposed, since it closely resembles a new roll of film. Inadvertently loading such a previously used film cartridge results in multiply-exposed film. As a result, many pictures are lost due to inadvertent loading of previously used film cartridges.
Moreover, many pictures are lost due to exposed film not being developed in a timely manner. As conventional film cartridges have no means of easily indicating a manufacturing date, or a date by which it is best to develop the film, manufacturers have not been able to inexpensively add a date indication to their film products.
U.S. Pat. No. 4,994,828 to Smart on FIG. 19, 1992, teaches a camera apparatus for preventing the loading of exposed film. Such devices need to be built into the camera, and only work with a particular type of film cartridge. Such devices, therefore, are of no use to those whom already have cameras, or those whom wish to use conventional film cartridges. Moreover, such devices serve to mechanically prevent the loading of previously exposed film. Such mechanical devices are extremely expensive to develop and manufacture, and are prone to mechanical jamming and failure. Since competition in the camera market is strong, any additional devices included with a camera must provide considerable benefit versus cost. As such, prior art devices of this type have not been incorporated into many cameras.
Clearly, then, a device is needed for indicating both whether or not a film cartridge has been previously loaded into a camera, and when the film was manufactured or by when the film should be developed. Such a needed device would be extremely inexpensive and easy to manufacture and install on film cartridges. The present invention fulfills these needs and provides further related advantages.